Patent GB-1260267-A (GB)
Title: Method of providing a printed circuit on a coherent memory plate having store and switching elements
IPC: H01F41/04
Filed: 1970-04-07
Abstract: 1,260,267. Magnetic storage apparatus. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 7 April, 1970 [10 April, 1969], No. 16341/70. Heading H3B. [Also in Divisions C7 and H1] A printed circuit is formed on an apertured plate of magnetic storage material without disturbing the magnetic characteristics by non- uniform mechanical stresses, the plate being completely embedded in a layer of a photo-resist which is subsequently hardened by exposure to light, and the printed circuit being bonded to the photo-resist layer by an intermediate layer of adhesive which hardens at below 130‹ C. A part 1, Fig. 1, of the plate of storage material may be apertured so as to provide word rows of three hole storage elements 3, and the other part 2 shaped to define elongate single hole word selection switch elements 6, 7, the printed circuit comprising conductors 4 which extend adjacent to the storage elements and conductors 5, 10 which pass about the limbs 11, 12 of the selection switch elements. Such a composite structure is disclosed in Specification 1,123,537. In one example of forming a printed circuit, a degreased permalloy memory plate is sprayed with a polyvinyl cinnamate photo-resist diluted with xylene, and the photo-resist layer so formed is hardened by ultraviolet light. The adhesive layer is then applied by spraying an adhesive solution comprising a part thermoplastic and part thermosetting adhesive composition diluted with cyclohexanone and methyl isobutyl, this layer being partially hardened by heating at 70‹ C. for 30 minutes. The adhesive layer is chemical roughened by applying a 6 molar HNO 3  solution, and a catalytically acting layer is then formed by immersion in a tank containing SnCl 2  and concentrated HCl in water, immersing in an aqueous solution of AgNO 3 , and finally immersing in an activating bath containing PdCl 2  and HCl, each process being followed by rinsing in deionized water. The catalytic layer so formed is intensified by copper electroless deposition, followed by copper electroplating, the final deposition process being followed by light etching using an H 2 SO 4  bath. A sprayed layer of a positive photo-resist is next applied and when dry is exposed behind a negative of the desired printing pattern. Following removal of the photo-resist from the exposed areas, the copper is selectively etched away by using a sprayed solution of FeCl 3 . Optionally the photo-resist remaining is removed by ethanol. An alternative process is to apply a photo-resist resistant to electro-plating immediately following the stage where a thin copper layer is electro-less deposited. This photo-resist is exposed and the desired wiring pattern then built up by electroplating. Finally the photoresist still present is removed and the thin copper layer exposed removed by etching. In a second example of forming a printed circuit, the adhesive layer is made photo-sensitive by the inclusion of TiC 2 , the adhesive comprising epoxy resin with butadiene-acrylonitrile in methyl isobutyl ketone and cyclohexanone. After partial hardening at 70‹ C. the sheet is immersed in an aqueous solution of PdCl 2  and concentrated HCl and then dried in hot air. The adhesive is then selectively exposed to light using a wiring pattern negative and the latent image consisting of Pd-nuclei intensified by electro-less copper plating after rinsing off the unwanted palladium salt. The Specification discloses other compositions of adhesive and details of suitable photoresist and electro-less baths.